// File: contracts/ERC1155/ERC1155NFTContract.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;

import "./ERC1155NFTBase.sol";
import "../ChainLinkRandom.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import "@openzeppelin/contracts/utils/Strings.sol";

contract ERC1155NFTContract is
    ERC1155NFTBase,
    ChainLinkRandom,
    ReentrancyGuard
{
    using Strings for uint256;

    bool internal revealed;

    constructor(
        address _VRFCoordinator,
        address _LINKToken,
        bytes32 _keyHash,
        string memory _blankURI,
        uint256 _supply,
        uint256 _price,
        uint256 _maxMint
    )
        public
        ERC1155NFTBase(_blankURI, _supply, _price, _maxMint)
        ChainLinkRandom(_VRFCoordinator, _LINKToken, _keyHash)
    {}

    /**
     * @dev reveal metadata of tokens.
     * @dev only can call one time, and only owner can call it.
     * @dev function will request to chainlink oracle and receive random number.
     * @dev contract will get this number by fulfillRandomness function.
     * @dev You should transfer 2 LINK token to contract, before call this function
     */
    function reveal() public onlyOwner {
        require(!revealed, "You have already generated a random seed");
        require(
            bytes(baseMetadataURI).length > 0,
            "You should set baseURI first"
        );
        revealed = true;
        _generateRandomSeed();
    }

    /**
     * @dev query metadata id of token
     * @notice only know after owner owner create `seed`
     * @param tokenId The id of token you want to query
     */
    function deterministic(uint256 tokenId)
        internal
        view
        returns (string memory)
    {
        uint256[] memory metaIds = new uint256[](TOTAL_SUPPLY);
        uint256[] memory randomArray = new uint256[](8);

        for (uint256 i = 0; i < TOTAL_SUPPLY; i++) {
            metaIds[i] = i;
        }

        // shuffle meta id
        for (uint256 i = 0; i < TOTAL_SUPPLY; i++) {
            /**
             * Get 256 bit random number
             * Split it into 8 parts (32 bit random number)
             */
            if (i % 8 == 0) {
                uint256 randomNumber = generateRandomNumber(i);
                randomArray[0] =
                    uint256(
                        randomNumber &
                            0xffffffff00000000000000000000000000000000000000000000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[1] =
                    uint256(
                        randomNumber &
                            0x00000000ffffffff000000000000000000000000000000000000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[2] =
                    uint256(
                        randomNumber &
                            0x0000000000000000ffffffff0000000000000000000000000000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[3] =
                    uint256(
                        randomNumber &
                            0x000000000000000000000000ffffffff00000000000000000000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[4] =
                    uint256(
                        randomNumber &
                            0x00000000000000000000000000000000ffffffff000000000000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[5] =
                    uint256(
                        randomNumber &
                            0x0000000000000000000000000000000000000000ffffffff0000000000000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[6] =
                    uint256(
                        randomNumber &
                            0x000000000000000000000000000000000000000000000000ffffffff00000000
                    ) %
                    (TOTAL_SUPPLY);
                randomArray[7] =
                    uint256(
                        randomNumber &
                            0x00000000000000000000000000000000000000000000000000000000ffffffff
                    ) %
                    (TOTAL_SUPPLY);
            }

            uint256 j = randomArray[i % 8];
            (metaIds[i], metaIds[j]) = (metaIds[j], metaIds[i]);
        }

        return metaIds[tokenId].toString();
    }

    /**
     * @dev query tokenURI of token Id
     * @dev before reveal will return default URI
     * @dev after reveal return token URI of this token on IPFS
     * @param tokenId The id of token you want to query
     */

    function uri(uint256 tokenId)
        external
        view
        virtual
        override
        returns (string memory)
    {
        require(tokenId < nextIndex(), "URI query for nonexistant token");

        // before reveal, nobody know what happened. Return _blankURI
        if (seed == 0) {
            return blankURI;
        }

        // after reveal, you can know your know.
        return
            string(abi.encodePacked(baseMetadataURI, deterministic(tokenId)));
    }

    /**
     * @dev mint token in sale period
     */
    function mintTokenOnSale(uint256 numberToken)
        external
        payable
        nonReentrant
        mintable(numberToken)
    {
        _mintOnSale(_msgSender(), numberToken);
    }

    /**
     * @dev mint token in pre sale period
     */
    function mintTokenOnPreSale(uint256 numberToken)
        external
        payable
        nonReentrant
        mintable(numberToken)
    {
        _mintPreSale(_msgSender(), numberToken);
    }

    /**
     * @dev Airdrop ether to a list of address
     * @param _to List of address
     * @param _value List of value
     */
    function multiAirdrop(address[] calldata _to, uint256[] calldata _value)
        public
        onlyOwner
        returns (bool _success)
    {
        // input validation
        assert(_to.length == _value.length);
        assert(_to.length <= 255);

        // loop through to addresses and send value
        for (uint8 i = 0; i < _to.length; i++) {
            payable(_to[i]).transfer(_value[i]);
        }

        return true;
    }
}

// File: contracts/ERC1155/ERC1155NFTBase.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";

/**
 * @dev ERC1155NFTBase contract.
 * @notice Setup admin control functional, include price,
 */
contract ERC1155NFTBase is Ownable, ERC1155 {
    // status of contract
    enum STATUS {
        OFF_SALE,
        PRE_SALE,
        ON_SALE
    }

    enum STAGE {
        STAGE_1,
        STAGE_2,
        STAGE_3,
        SOLD_ALL
    }

    // index of next token aka number of token was minted
    uint256 private _nextIndex;

    // maximum token can be minted
    uint256 public TOTAL_SUPPLY;

    // maximum token can be minted per wallet
    uint256 public maxMint;
    uint256 public price;

    // URI of token before reveal
    string internal blankURI;

    string internal baseMetadataURI;

    STATUS public status;
    STAGE public stage;
    mapping(address => bool) public whitelist;
    mapping(address => uint256) public counter;

    constructor(
        string memory _blankURI,
        uint256 _supply,
        uint256 _price,
        uint256 _maxMint
    ) public ERC1155(_blankURI) {
        _nextIndex = 0;
        TOTAL_SUPPLY = _supply;
        price = _price;
        maxMint = _maxMint;
        blankURI = _blankURI;
        stage = STAGE.STAGE_1;
    }

    /**
     * @dev ensure collector pays for mint token
     */
    modifier mintable(uint256 _number) {
        require(
            _number.add(nextIndex()) <= TOTAL_SUPPLY,
            "Bound limit of maximum supply limit"
        );
        _;
    }

    /**
     * @dev next token index.
     */
    function nextIndex() public view virtual returns (uint256) {
        return _nextIndex;
    }

    /**
     * @dev change status from online to offline and vice versa
     */
    function setStatus(STATUS _status) public onlyOwner returns (bool) {
        status = _status;
        return true;
    }

    function setStatusWithPriceAndMaxMint(
        STATUS _status,
        uint256 _price,
        uint256 _maxMint
    ) public onlyOwner returns (bool) {
        status = _status;
        price = _price;
        maxMint = _maxMint;
        return true;
    }

    function setStage(STAGE _stage) public onlyOwner returns (bool) {
        stage = _stage;
        return true;
    }

    function setPrice(uint256 _price) public onlyOwner {
        price = _price;
    }

    function setMaxMint(uint256 _maxMint) external onlyOwner {
        maxMint = _maxMint;
    }

    function setBaseURI(string memory _baseURI) public onlyOwner {
        baseMetadataURI = _baseURI;
    }

    function setBlankURI(string memory _blankURI) public onlyOwner {
        blankURI = _blankURI;
    }

    function addToWhitelist(address[] memory _wallets) public onlyOwner {
        for (uint256 i = 0; i < _wallets.length; ++i) {
            whitelist[_wallets[i]] = true;
        }
    }

    function removeFromWhitelist(address[] memory _wallets) public onlyOwner {
        for (uint256 i = 0; i < _wallets.length; ++i) {
            whitelist[_wallets[i]] = false;
        }
    }

    function withdraw() public onlyOwner {
        uint256 balance = address(this).balance;
        payable(msg.sender).transfer(balance);
    }

    function _mintToken(address _receiver, uint256 _number) internal {
        if (stage == STAGE.STAGE_1) {
            require(
                _number.add(nextIndex()) <= 2000,
                "Bound limit of maximum supply of Stage 1"
            );
        }
        if (stage == STAGE.STAGE_2) {
            require(
                _number.add(nextIndex()) <= 6000,
                "Bound limit of maximum supply of Stage 2"
            );
        }
        uint256[] memory ids = new uint256[](_number);
        uint256[] memory amounts = new uint256[](_number);

        for (uint256 i = 0; i < _number; i++) {
            ids[i] = nextIndex();
            amounts[i] = 1;
            _nextIndex = _nextIndex.add(1);
        }

        _mintBatch(_receiver, ids, amounts, "");

        counter[_receiver] = counter[_receiver].add(_number);
    }

    function _mintOnSale(address _receiver, uint256 _numTokensToMint) internal {
        require(status == STATUS.ON_SALE, "Status is not on sale");
        require(msg.value >= _numTokensToMint.mul(price), "Payment error");
        require(
            _numTokensToMint.add(counter[_receiver]) <= maxMint,
            "Over max token can mint per wallet"
        );

        _mintToken(_receiver, _numTokensToMint);
    }

    function _mintPreSale(address _receiver, uint256 _numTokensToMint)
        internal
    {
        require(status == STATUS.PRE_SALE, "Status is not preSale");
        require(whitelist[_receiver], "You are not in whitelist");
        require(msg.value >= _numTokensToMint.mul(price), "Payment error");
        require(
            _numTokensToMint.add(counter[_receiver]) <= maxMint,
            "Over max token can mint per wallet"
        );

        _mintToken(_receiver, _numTokensToMint);
    }
}

// File: contracts/ChainLinkRandom.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

import "@chainlink/contracts/src/v0.6/VRFConsumerBase.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract ChainLinkRandom is Ownable, VRFConsumerBase {
    event TokenSeed(uint256 seed);

    uint256 public seed;

    uint256 internal fee;
    bytes32 internal keyHash;

    bytes32 private _requestId;
    bool private _requesting;

    constructor(
        address _VRFCoordinator,
        address _LINKToken,
        bytes32 _keyHash
    ) public VRFConsumerBase(_VRFCoordinator, _LINKToken) {
        keyHash = _keyHash;
        fee = 2 * 10**18; // 2 LINK token
        _requesting = false;
        seed = 0;
    }

    /**
     * @dev backup seed generator if the ChainLink is experiencing difficulties
     */
    function feedSeed() external onlyOwner {
        require(_requesting == true, "not requesting");
        require(seed == 0, "received random number");
        _requesting = false;
        seed = uint256(blockhash(block.number - 1));
        emit TokenSeed(seed);
    }

    /**
     * @dev receive random number from chainlink
     * @notice random number will greater than zero
     */
    function fulfillRandomness(bytes32 requestId, uint256 randomNumber)
        internal
        override
    {
        require(_requesting == true, "not requesting");
        require(requestId == _requestId, "not my request");
        _requesting = false;
        if (randomNumber > 0) seed = randomNumber;
        else seed = 1;
        emit TokenSeed(seed);
    }

    function _generateRandomSeed() internal {
        require(LINK.balanceOf(address(this)) >= fee, "not enought LINK token");
        _requestId = requestRandomness(keyHash, fee);
        _requesting = true;
    }

    /**
     * @dev compute element with shuffle with id
     */
    function shuffleId(
        uint256 _TOTAL_SUPPLY,
        uint256 _id,
        uint256 _start
    ) internal view returns (uint256) {
        uint256 random = generateRandomNumber(_id);
        return random.mod(_TOTAL_SUPPLY.sub(_start)).add(_start);
    }

    /**
     * @dev return random number from seed and _id
     */
    function generateRandomNumber(uint256 _id) internal view returns (uint256) {
        return uint256(keccak256(abi.encode(seed, _id)));
    }

    function withdrawLink() external onlyOwner {
        LINK.transfer(owner(), LINK.balanceOf(address(this)));
    }
}

// File: @openzeppelin/contracts/utils/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () internal {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    /**
     * @dev Converts a `uint256` to its ASCII `string` representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = bytes1(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC1155.sol";
import "./IERC1155MetadataURI.sol";
import "./IERC1155Receiver.sol";
import "../../utils/Context.sol";
import "../../introspection/ERC165.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 *
 * @dev Implementation of the basic standard multi-token.
 * See https://eips.ethereum.org/EIPS/eip-1155
 * Originally based on code by Enjin: https://github.com/enjin/erc-1155
 *
 * _Available since v3.1._
 */
contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
    using SafeMath for uint256;
    using Address for address;

    // Mapping from token ID to account balances
    mapping (uint256 => mapping(address => uint256)) private _balances;

    // Mapping from account to operator approvals
    mapping (address => mapping(address => bool)) private _operatorApprovals;

    // Used as the URI for all token types by relying on ID substitution, e.g. https://token-cdn-domain/{id}.json
    string private _uri;

    /*
     *     bytes4(keccak256('balanceOf(address,uint256)')) == 0x00fdd58e
     *     bytes4(keccak256('balanceOfBatch(address[],uint256[])')) == 0x4e1273f4
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,uint256,bytes)')) == 0xf242432a
     *     bytes4(keccak256('safeBatchTransferFrom(address,address,uint256[],uint256[],bytes)')) == 0x2eb2c2d6
     *
     *     => 0x00fdd58e ^ 0x4e1273f4 ^ 0xa22cb465 ^
     *        0xe985e9c5 ^ 0xf242432a ^ 0x2eb2c2d6 == 0xd9b67a26
     */
    bytes4 private constant _INTERFACE_ID_ERC1155 = 0xd9b67a26;

    /*
     *     bytes4(keccak256('uri(uint256)')) == 0x0e89341c
     */
    bytes4 private constant _INTERFACE_ID_ERC1155_METADATA_URI = 0x0e89341c;

    /**
     * @dev See {_setURI}.
     */
    constructor (string memory uri_) public {
        _setURI(uri_);

        // register the supported interfaces to conform to ERC1155 via ERC165
        _registerInterface(_INTERFACE_ID_ERC1155);

        // register the supported interfaces to conform to ERC1155MetadataURI via ERC165
        _registerInterface(_INTERFACE_ID_ERC1155_METADATA_URI);
    }

    /**
     * @dev See {IERC1155MetadataURI-uri}.
     *
     * This implementation returns the same URI for *all* token types. It relies
     * on the token type ID substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * Clients calling this function must replace the `\{id\}` substring with the
     * actual token type ID.
     */
    function uri(uint256) external view virtual override returns (string memory) {
        return _uri;
    }

    /**
     * @dev See {IERC1155-balanceOf}.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) public view virtual override returns (uint256) {
        require(account != address(0), "ERC1155: balance query for the zero address");
        return _balances[id][account];
    }

    /**
     * @dev See {IERC1155-balanceOfBatch}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(
        address[] memory accounts,
        uint256[] memory ids
    )
        public
        view
        virtual
        override
        returns (uint256[] memory)
    {
        require(accounts.length == ids.length, "ERC1155: accounts and ids length mismatch");

        uint256[] memory batchBalances = new uint256[](accounts.length);

        for (uint256 i = 0; i < accounts.length; ++i) {
            batchBalances[i] = balanceOf(accounts[i], ids[i]);
        }

        return batchBalances;
    }

    /**
     * @dev See {IERC1155-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(_msgSender() != operator, "ERC1155: setting approval status for self");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC1155-isApprovedForAll}.
     */
    function isApprovedForAll(address account, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[account][operator];
    }

    /**
     * @dev See {IERC1155-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    )
        public
        virtual
        override
    {
        require(to != address(0), "ERC1155: transfer to the zero address");
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: caller is not owner nor approved"
        );

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), data);

        _balances[id][from] = _balances[id][from].sub(amount, "ERC1155: insufficient balance for transfer");
        _balances[id][to] = _balances[id][to].add(amount);

        emit TransferSingle(operator, from, to, id, amount);

        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
    }

    /**
     * @dev See {IERC1155-safeBatchTransferFrom}.
     */
    function safeBatchTransferFrom(
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        public
        virtual
        override
    {
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
        require(to != address(0), "ERC1155: transfer to the zero address");
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: transfer caller is not owner nor approved"
        );

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, to, ids, amounts, data);

        for (uint256 i = 0; i < ids.length; ++i) {
            uint256 id = ids[i];
            uint256 amount = amounts[i];

            _balances[id][from] = _balances[id][from].sub(
                amount,
                "ERC1155: insufficient balance for transfer"
            );
            _balances[id][to] = _balances[id][to].add(amount);
        }

        emit TransferBatch(operator, from, to, ids, amounts);

        _doSafeBatchTransferAcceptanceCheck(operator, from, to, ids, amounts, data);
    }

    /**
     * @dev Sets a new URI for all token types, by relying on the token type ID
     * substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * By this mechanism, any occurrence of the `\{id\}` substring in either the
     * URI or any of the amounts in the JSON file at said URI will be replaced by
     * clients with the token type ID.
     *
     * For example, the `https://token-cdn-domain/\{id\}.json` URI would be
     * interpreted by clients as
     * `https://token-cdn-domain/000000000000000000000000000000000000000000000000000000000004cce0.json`
     * for token type ID 0x4cce0.
     *
     * See {uri}.
     *
     * Because these URIs cannot be meaningfully represented by the {URI} event,
     * this function emits no events.
     */
    function _setURI(string memory newuri) internal virtual {
        _uri = newuri;
    }

    /**
     * @dev Creates `amount` tokens of token type `id`, and assigns them to `account`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - If `account` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function _mint(address account, uint256 id, uint256 amount, bytes memory data) internal virtual {
        require(account != address(0), "ERC1155: mint to the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), account, _asSingletonArray(id), _asSingletonArray(amount), data);

        _balances[id][account] = _balances[id][account].add(amount);
        emit TransferSingle(operator, address(0), account, id, amount);

        _doSafeTransferAcceptanceCheck(operator, address(0), account, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_mint}.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function _mintBatch(address to, uint256[] memory ids, uint256[] memory amounts, bytes memory data) internal virtual {
        require(to != address(0), "ERC1155: mint to the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), to, ids, amounts, data);

        for (uint i = 0; i < ids.length; i++) {
            _balances[ids[i]][to] = amounts[i].add(_balances[ids[i]][to]);
        }

        emit TransferBatch(operator, address(0), to, ids, amounts);

        _doSafeBatchTransferAcceptanceCheck(operator, address(0), to, ids, amounts, data);
    }

    /**
     * @dev Destroys `amount` tokens of token type `id` from `account`
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens of token type `id`.
     */
    function _burn(address account, uint256 id, uint256 amount) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), _asSingletonArray(id), _asSingletonArray(amount), "");

        _balances[id][account] = _balances[id][account].sub(
            amount,
            "ERC1155: burn amount exceeds balance"
        );

        emit TransferSingle(operator, account, address(0), id, amount);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_burn}.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     */
    function _burnBatch(address account, uint256[] memory ids, uint256[] memory amounts) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), ids, amounts, "");

        for (uint i = 0; i < ids.length; i++) {
            _balances[ids[i]][account] = _balances[ids[i]][account].sub(
                amounts[i],
                "ERC1155: burn amount exceeds balance"
            );
        }

        emit TransferBatch(operator, account, address(0), ids, amounts);
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning, as well as batched variants.
     *
     * The same hook is called on both single and batched variants. For single
     * transfers, the length of the `id` and `amount` arrays will be 1.
     *
     * Calling conditions (for each `id` and `amount` pair):
     *
     * - When `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * of token type `id` will be  transferred to `to`.
     * - When `from` is zero, `amount` tokens of token type `id` will be minted
     * for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens of token type `id`
     * will be burned.
     * - `from` and `to` are never both zero.
     * - `ids` and `amounts` have the same, non-zero length.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        internal
        virtual
    { }

    function _doSafeTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    )
        private
    {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155Received(operator, from, id, amount, data) returns (bytes4 response) {
                if (response != IERC1155Receiver(to).onERC1155Received.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non ERC1155Receiver implementer");
            }
        }
    }

    function _doSafeBatchTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        private
    {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155BatchReceived(operator, from, ids, amounts, data) returns (bytes4 response) {
                if (response != IERC1155Receiver(to).onERC1155BatchReceived.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non ERC1155Receiver implementer");
            }
        }
    }

    function _asSingletonArray(uint256 element) private pure returns (uint256[] memory) {
        uint256[] memory array = new uint256[](1);
        array[0] = element;

        return array;
    }
}

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "../../introspection/IERC165.sol";

/**
 * @dev Required interface of an ERC1155 compliant contract, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1155[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155 is IERC165 {
    /**
     * @dev Emitted when `value` tokens of token type `id` are transferred from `from` to `to` by `operator`.
     */
    event TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value);

    /**
     * @dev Equivalent to multiple {TransferSingle} events, where `operator`, `from` and `to` are the same for all
     * transfers.
     */
    event TransferBatch(address indexed operator, address indexed from, address indexed to, uint256[] ids, uint256[] values);

    /**
     * @dev Emitted when `account` grants or revokes permission to `operator` to transfer their tokens, according to
     * `approved`.
     */
    event ApprovalForAll(address indexed account, address indexed operator, bool approved);

    /**
     * @dev Emitted when the URI for token type `id` changes to `value`, if it is a non-programmatic URI.
     *
     * If an {URI} event was emitted for `id`, the standard
     * https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[guarantees] that `value` will equal the value
     * returned by {IERC1155MetadataURI-uri}.
     */
    event URI(string value, uint256 indexed id);

    /**
     * @dev Returns the amount of tokens of token type `id` owned by `account`.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) external view returns (uint256);

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {balanceOf}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(address[] calldata accounts, uint256[] calldata ids) external view returns (uint256[] memory);

    /**
     * @dev Grants or revokes permission to `operator` to transfer the caller's tokens, according to `approved`,
     *
     * Emits an {ApprovalForAll} event.
     *
     * Requirements:
     *
     * - `operator` cannot be the caller.
     */
    function setApprovalForAll(address operator, bool approved) external;

    /**
     * @dev Returns true if `operator` is approved to transfer ``account``'s tokens.
     *
     * See {setApprovalForAll}.
     */
    function isApprovedForAll(address account, address operator) external view returns (bool);

    /**
     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - If the caller is not `from`, it must be have been approved to spend ``from``'s tokens via {setApprovalForAll}.
     * - `from` must have a balance of tokens of type `id` of at least `amount`.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes calldata data) external;

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {safeTransferFrom}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function safeBatchTransferFrom(address from, address to, uint256[] calldata ids, uint256[] calldata amounts, bytes calldata data) external;
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155MetadataURI.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC1155.sol";

/**
 * @dev Interface of the optional ERC1155MetadataExtension interface, as defined
 * in the https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155MetadataURI is IERC1155 {
    /**
     * @dev Returns the URI for token type `id`.
     *
     * If the `\{id\}` substring is present in the URI, it must be replaced by
     * clients with the actual token type ID.
     */
    function uri(uint256 id) external view returns (string memory);
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../introspection/IERC165.sol";

/**
 * _Available since v3.1._
 */
interface IERC1155Receiver is IERC165 {

    /**
        @dev Handles the receipt of a single ERC1155 token type. This function is
        called at the end of a `safeTransferFrom` after the balance has been updated.
        To accept the transfer, this must return
        `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))`
        (i.e. 0xf23a6e61, or its own function selector).
        @param operator The address which initiated the transfer (i.e. msg.sender)
        @param from The address which previously owned the token
        @param id The ID of the token being transferred
        @param value The amount of tokens being transferred
        @param data Additional data with no specified format
        @return `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))` if transfer is allowed
    */
    function onERC1155Received(
        address operator,
        address from,
        uint256 id,
        uint256 value,
        bytes calldata data
    )
        external
        returns(bytes4);

    /**
        @dev Handles the receipt of a multiple ERC1155 token types. This function
        is called at the end of a `safeBatchTransferFrom` after the balances have
        been updated. To accept the transfer(s), this must return
        `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))`
        (i.e. 0xbc197c81, or its own function selector).
        @param operator The address which initiated the batch transfer (i.e. msg.sender)
        @param from The address which previously owned the token
        @param ids An array containing ids of each token being transferred (order and length must match values array)
        @param values An array containing amounts of each token being transferred (order and length must match ids array)
        @param data Additional data with no specified format
        @return `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))` if transfer is allowed
    */
    function onERC1155BatchReceived(
        address operator,
        address from,
        uint256[] calldata ids,
        uint256[] calldata values,
        bytes calldata data
    )
        external
        returns(bytes4);
}

// File: @openzeppelin/contracts/introspection/ERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor () internal {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }

    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) return (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/introspection/IERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @chainlink/contracts/src/v0.6/VRFConsumerBase.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "./vendor/SafeMathChainlink.sol";

import "./interfaces/LinkTokenInterface.sol";

import "./VRFRequestIDBase.sol";

/** ****************************************************************************
 * @notice Interface for contracts using VRF randomness
 * *****************************************************************************
 * @dev PURPOSE
 *
 * @dev Reggie the Random Oracle (not his real job) wants to provide randomness
 * @dev to Vera the verifier in such a way that Vera can be sure he's not
 * @dev making his output up to suit himself. Reggie provides Vera a public key
 * @dev to which he knows the secret key. Each time Vera provides a seed to
 * @dev Reggie, he gives back a value which is computed completely
 * @dev deterministically from the seed and the secret key.
 *
 * @dev Reggie provides a proof by which Vera can verify that the output was
 * @dev correctly computed once Reggie tells it to her, but without that proof,
 * @dev the output is indistinguishable to her from a uniform random sample
 * @dev from the output space.
 *
 * @dev The purpose of this contract is to make it easy for unrelated contracts
 * @dev to talk to Vera the verifier about the work Reggie is doing, to provide
 * @dev simple access to a verifiable source of randomness.
 * *****************************************************************************
 * @dev USAGE
 *
 * @dev Calling contracts must inherit from VRFConsumerBase, and can
 * @dev initialize VRFConsumerBase's attributes in their constructor as
 * @dev shown:
 *
 * @dev   contract VRFConsumer {
 * @dev     constuctor(<other arguments>, address _vrfCoordinator, address _link)
 * @dev       VRFConsumerBase(_vrfCoordinator, _link) public {
 * @dev         <initialization with other arguments goes here>
 * @dev       }
 * @dev   }
 *
 * @dev The oracle will have given you an ID for the VRF keypair they have
 * @dev committed to (let's call it keyHash), and have told you the minimum LINK
 * @dev price for VRF service. Make sure your contract has sufficient LINK, and
 * @dev call requestRandomness(keyHash, fee, seed), where seed is the input you
 * @dev want to generate randomness from.
 *
 * @dev Once the VRFCoordinator has received and validated the oracle's response
 * @dev to your request, it will call your contract's fulfillRandomness method.
 *
 * @dev The randomness argument to fulfillRandomness is the actual random value
 * @dev generated from your seed.
 *
 * @dev The requestId argument is generated from the keyHash and the seed by
 * @dev makeRequestId(keyHash, seed). If your contract could have concurrent
 * @dev requests open, you can use the requestId to track which seed is
 * @dev associated with which randomness. See VRFRequestIDBase.sol for more
 * @dev details. (See "SECURITY CONSIDERATIONS" for principles to keep in mind,
 * @dev if your contract could have multiple requests in flight simultaneously.)
 *
 * @dev Colliding `requestId`s are cryptographically impossible as long as seeds
 * @dev differ. (Which is critical to making unpredictable randomness! See the
 * @dev next section.)
 *
 * *****************************************************************************
 * @dev SECURITY CONSIDERATIONS
 *
 * @dev A method with the ability to call your fulfillRandomness method directly
 * @dev could spoof a VRF response with any random value, so it's critical that
 * @dev it cannot be directly called by anything other than this base contract
 * @dev (specifically, by the VRFConsumerBase.rawFulfillRandomness method).
 *
 * @dev For your users to trust that your contract's random behavior is free
 * @dev from malicious interference, it's best if you can write it so that all
 * @dev behaviors implied by a VRF response are executed *during* your
 * @dev fulfillRandomness method. If your contract must store the response (or
 * @dev anything derived from it) and use it later, you must ensure that any
 * @dev user-significant behavior which depends on that stored value cannot be
 * @dev manipulated by a subsequent VRF request.
 *
 * @dev Similarly, both miners and the VRF oracle itself have some influence
 * @dev over the order in which VRF responses appear on the blockchain, so if
 * @dev your contract could have multiple VRF requests in flight simultaneously,
 * @dev you must ensure that the order in which the VRF responses arrive cannot
 * @dev be used to manipulate your contract's user-significant behavior.
 *
 * @dev Since the ultimate input to the VRF is mixed with the block hash of the
 * @dev block in which the request is made, user-provided seeds have no impact
 * @dev on its economic security properties. They are only included for API
 * @dev compatability with previous versions of this contract.
 *
 * @dev Since the block hash of the block which contains the requestRandomness
 * @dev call is mixed into the input to the VRF *last*, a sufficiently powerful
 * @dev miner could, in principle, fork the blockchain to evict the block
 * @dev containing the request, forcing the request to be included in a
 * @dev different block with a different hash, and therefore a different input
 * @dev to the VRF. However, such an attack would incur a substantial economic
 * @dev cost. This cost scales with the number of blocks the VRF oracle waits
 * @dev until it calls responds to a request.
 */
abstract contract VRFConsumerBase is VRFRequestIDBase {

  using SafeMathChainlink for uint256;

  /**
   * @notice fulfillRandomness handles the VRF response. Your contract must
   * @notice implement it. See "SECURITY CONSIDERATIONS" above for important
   * @notice principles to keep in mind when implementing your fulfillRandomness
   * @notice method.
   *
   * @dev VRFConsumerBase expects its subcontracts to have a method with this
   * @dev signature, and will call it once it has verified the proof
   * @dev associated with the randomness. (It is triggered via a call to
   * @dev rawFulfillRandomness, below.)
   *
   * @param requestId The Id initially returned by requestRandomness
   * @param randomness the VRF output
   */
  function fulfillRandomness(bytes32 requestId, uint256 randomness)
    internal virtual;

  /**
   * @dev In order to keep backwards compatibility we have kept the user
   * seed field around. We remove the use of it because given that the blockhash
   * enters later, it overrides whatever randomness the used seed provides.
   * Given that it adds no security, and can easily lead to misunderstandings,
   * we have removed it from usage and can now provide a simpler API.
   */
  uint256 constant private USER_SEED_PLACEHOLDER = 0;

  /**
   * @notice requestRandomness initiates a request for VRF output given _seed
   *
   * @dev The fulfillRandomness method receives the output, once it's provided
   * @dev by the Oracle, and verified by the vrfCoordinator.
   *
   * @dev The _keyHash must already be registered with the VRFCoordinator, and
   * @dev the _fee must exceed the fee specified during registration of the
   * @dev _keyHash.
   *
   * @dev The _seed parameter is vestigial, and is kept only for API
   * @dev compatibility with older versions. It can't *hurt* to mix in some of
   * @dev your own randomness, here, but it's not necessary because the VRF
   * @dev oracle will mix the hash of the block containing your request into the
   * @dev VRF seed it ultimately uses.
   *
   * @param _keyHash ID of public key against which randomness is generated
   * @param _fee The amount of LINK to send with the request
   *
   * @return requestId unique ID for this request
   *
   * @dev The returned requestId can be used to distinguish responses to
   * @dev concurrent requests. It is passed as the first argument to
   * @dev fulfillRandomness.
   */
  function requestRandomness(bytes32 _keyHash, uint256 _fee)
    internal returns (bytes32 requestId)
  {
    LINK.transferAndCall(vrfCoordinator, _fee, abi.encode(_keyHash, USER_SEED_PLACEHOLDER));
    // This is the seed passed to VRFCoordinator. The oracle will mix this with
    // the hash of the block containing this request to obtain the seed/input
    // which is finally passed to the VRF cryptographic machinery.
    uint256 vRFSeed  = makeVRFInputSeed(_keyHash, USER_SEED_PLACEHOLDER, address(this), nonces[_keyHash]);
    // nonces[_keyHash] must stay in sync with
    // VRFCoordinator.nonces[_keyHash][this], which was incremented by the above
    // successful LINK.transferAndCall (in VRFCoordinator.randomnessRequest).
    // This provides protection against the user repeating their input seed,
    // which would result in a predictable/duplicate output, if multiple such
    // requests appeared in the same block.
    nonces[_keyHash] = nonces[_keyHash].add(1);
    return makeRequestId(_keyHash, vRFSeed);
  }

  LinkTokenInterface immutable internal LINK;
  address immutable private vrfCoordinator;

  // Nonces for each VRF key from which randomness has been requested.
  //
  // Must stay in sync with VRFCoordinator[_keyHash][this]
  mapping(bytes32 /* keyHash */ => uint256 /* nonce */) private nonces;

  /**
   * @param _vrfCoordinator address of VRFCoordinator contract
   * @param _link address of LINK token contract
   *
   * @dev https://docs.chain.link/docs/link-token-contracts
   */
  constructor(address _vrfCoordinator, address _link) public {
    vrfCoordinator = _vrfCoordinator;
    LINK = LinkTokenInterface(_link);
  }

  // rawFulfillRandomness is called by VRFCoordinator when it receives a valid VRF
  // proof. rawFulfillRandomness then calls fulfillRandomness, after validating
  // the origin of the call
  function rawFulfillRandomness(bytes32 requestId, uint256 randomness) external {
    require(msg.sender == vrfCoordinator, "Only VRFCoordinator can fulfill");
    fulfillRandomness(requestId, randomness);
  }
}

// File: @chainlink/contracts/src/v0.6/vendor/SafeMathChainlink.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMathChainlink {
  /**
    * @dev Returns the addition of two unsigned integers, reverting on
    * overflow.
    *
    * Counterpart to Solidity's `+` operator.
    *
    * Requirements:
    * - Addition cannot overflow.
    */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");

    return c;
  }

  /**
    * @dev Returns the subtraction of two unsigned integers, reverting on
    * overflow (when the result is negative).
    *
    * Counterpart to Solidity's `-` operator.
    *
    * Requirements:
    * - Subtraction cannot overflow.
    */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a, "SafeMath: subtraction overflow");
    uint256 c = a - b;

    return c;
  }

  /**
    * @dev Returns the multiplication of two unsigned integers, reverting on
    * overflow.
    *
    * Counterpart to Solidity's `*` operator.
    *
    * Requirements:
    * - Multiplication cannot overflow.
    */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b, "SafeMath: multiplication overflow");

    return c;
  }

  /**
    * @dev Returns the integer division of two unsigned integers. Reverts on
    * division by zero. The result is rounded towards zero.
    *
    * Counterpart to Solidity's `/` operator. Note: this function uses a
    * `revert` opcode (which leaves remaining gas untouched) while Solidity
    * uses an invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    * - The divisor cannot be zero.
    */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // Solidity only automatically asserts when dividing by 0
    require(b > 0, "SafeMath: division by zero");
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
    * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
    * Reverts when dividing by zero.
    *
    * Counterpart to Solidity's `%` operator. This function uses a `revert`
    * opcode (which leaves remaining gas untouched) while Solidity uses an
    * invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    * - The divisor cannot be zero.
    */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0, "SafeMath: modulo by zero");
    return a % b;
  }
}

// File: @chainlink/contracts/src/v0.6/interfaces/LinkTokenInterface.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

interface LinkTokenInterface {
  function allowance(address owner, address spender) external view returns (uint256 remaining);
  function approve(address spender, uint256 value) external returns (bool success);
  function balanceOf(address owner) external view returns (uint256 balance);
  function decimals() external view returns (uint8 decimalPlaces);
  function decreaseApproval(address spender, uint256 addedValue) external returns (bool success);
  function increaseApproval(address spender, uint256 subtractedValue) external;
  function name() external view returns (string memory tokenName);
  function symbol() external view returns (string memory tokenSymbol);
  function totalSupply() external view returns (uint256 totalTokensIssued);
  function transfer(address to, uint256 value) external returns (bool success);
  function transferAndCall(address to, uint256 value, bytes calldata data) external returns (bool success);
  function transferFrom(address from, address to, uint256 value) external returns (bool success);
}

// File: @chainlink/contracts/src/v0.6/VRFRequestIDBase.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract VRFRequestIDBase {

  /**
   * @notice returns the seed which is actually input to the VRF coordinator
   *
   * @dev To prevent repetition of VRF output due to repetition of the
   * @dev user-supplied seed, that seed is combined in a hash with the
   * @dev user-specific nonce, and the address of the consuming contract. The
   * @dev risk of repetition is mostly mitigated by inclusion of a blockhash in
   * @dev the final seed, but the nonce does protect against repetition in
   * @dev requests which are included in a single block.
   *
   * @param _userSeed VRF seed input provided by user
   * @param _requester Address of the requesting contract
   * @param _nonce User-specific nonce at the time of the request
   */
  function makeVRFInputSeed(bytes32 _keyHash, uint256 _userSeed,
    address _requester, uint256 _nonce)
    internal pure returns (uint256)
  {
    return  uint256(keccak256(abi.encode(_keyHash, _userSeed, _requester, _nonce)));
  }

  /**
   * @notice Returns the id for this request
   * @param _keyHash The serviceAgreement ID to be used for this request
   * @param _vRFInputSeed The seed to be passed directly to the VRF
   * @return The id for this request
   *
   * @dev Note that _vRFInputSeed is not the seed passed by the consuming
   * @dev contract, but the one generated by makeVRFInputSeed
   */
  function makeRequestId(
    bytes32 _keyHash, uint256 _vRFInputSeed) internal pure returns (bytes32) {
    return keccak256(abi.encodePacked(_keyHash, _vRFInputSeed));
  }
}